1. Field of the Invention
The present invention relates to a measuring device having a transmitter side and a receiver side, said device being arranged for transmitting signals from the transmitter side to the receiver side via an optical connection.
2. Prior Art
It is known that measuring signals and other light signals can be transmitted via an optical link. Such a link comprises a light transmitter, light-transmitting members and light-detecting members. The light transmitter comprises members for modulation of the emitted light in a suitable manner such that the emitted light contains information about the present value of the measuring signal. The light-transmitting member, which may consist of one or more light conductors (optical fibers), transmits light signals to the detecting member, where information about the measuring signal is transformed into a suitable signal, for example into an electric voltage proportional to the measuring signal. A measuring device of this kind has several advantages. Galvanic separation is automatically obtained between the transmitter side and the receiver side, and therefore these sides may be located at completely different potential levels. The optical line is wholly insensitive to electromagnetic disturbances. In addition, no sparks or short-circuits may occur, which is of value, for example, in an explosive environment.
In a measuring device of the above-mentioned kind it is of considerable importance to reduce the power consumption on the transmitter side as far as possible, since the energy supply to the members of the transmitter side may present a problem, for example in those cases where these members are located at a high potential level.
In measuring at a high potential, it is a desire to dispense with the current and voltage transformers for high voltages which have been commonly used so far, but the transmission of energy from the receiver side to the transmitter side continues to be a problem.
In a measuring device for which a patent application has been filed in the United States by the same inventors (U.S. Ser. No. 75,873, filed Sept. 17, 1979) a measuring signal is transmitted from a transducer over a certain distance and/or a certain potential difference. The measuring device has a transmitter side, arranged in conjunction with the transducer, which is connected to a receiver side by an optical transmission link. The transmission side includes comparing members which compare measuring signals with a feed-back signal transmitted from the receiver side. The comparison result is transmitted to the receiver side, where it controls a regulator, the output signal of which constitutes the feed-back signal as well as the output signal of the measuring device. The measuring device further includes members for automatically maintaining the amplification in the transmission link for the feed-back signal constant. This device is a solution to the above-mentioned problems, and since only minor error signals are transmitted from the transmitter side to the receiver side the dynamic range of such transmission is low. The dynamic range of the total transmission is wholly determined by the dynamic range in the transmission of the feed-back signal from the receiver side to the transmitter side.